docs: def depth_score_helper(self, d, dopt):
          """
          Gets a weighted count of the number of Intervals deeper than dopt.
          :param d: current depth, starting from 0
          :param dopt: optimal maximum depth of a leaf Node
          :rtype: real
          """
          # di is how may levels deeper than optimal d is
          di = d - dopt
          if di > 0:
              count = di * len(self.s_center)
          else:
              count = 0
          if self.right_node:
              count += self.right_node.depth_score_helper(d + 1, dopt)
          if self.left_node:
              count += self.left_node.depth_score_helper(d + 1, dopt)
          return count